1. Field of the Invention
The present invention relates to a flexible wiring member on which a circuit element is mounted, and an electronic apparatus which connects an electrical load and an external signal source by the flexible wiring member.
2. Description of the Related Art
A jetting apparatus which jets liquid droplets is an example of an electronic apparatus. The jetting apparatus includes a jetting head in which nozzles for jetting the liquid droplets are formed. The jetting head includes an actuator as an electrical load, and the actuator has a drive portion corresponding to each of the nozzles. The liquid droplets are jetted from the nozzles by applying selectively a jetting pressure to a liquid inside the jetting head by the drive portion, based on a signal input to the drive portion of the actuator from an external signal source via a flexible wiring member. In such a jetting apparatus, when the number of nozzles is increased and the density of the nozzles becomes high, the density of the drive portions also becomes high. Accordingly, a wiring pattern of the flexible wiring member to be connected to the drive portions becomes fine, and a resistance of the wiring pattern becomes high. In the flexible wiring member, a circuit element which drives the actuator is mounted at a position as near as possible to the actuator in order to suppress the increase of the resistance.
As a flexible wiring member, a both-sides wired type, in which a wiring pattern is formed on both surfaces of a base layer, is available. However, there are problems such as a rise in a cost, and limitations on making fine a wiring pitch. Therefore, single-side wired material in which a wiring pattern is formed on one surface of a base layer has been generally used. The one-side wired material has electroconductive wires wired on one surface of a base layer which is made of an insulating resin material, and a covering layer made of an insulating resin is provided to cover the electroconductive wires. In the flexible wiring member, at a mounting position on which the circuit element is mounted, at a position on which an output electrode for connecting to an actuator is formed, and at a position on which an input electrode for connecting to an external signal source is formed, an electrode is formed by partially exposing the electroconductive wire by removing the base layer or the covering layer. Generally, polyimide is used as the base layer, and solder resist is used as the covering layer.
Incidentally, since the circuit element to be mounted on the flexible wiring member generates heat by driving the actuator, as in an ink-jet printer head described in Japanese Patent Application Laid-open No. 2007-83707 submitted by applicants of the present application, a damage due to transmission of the heat of the circuit toward the actuator is suppressed by arranging a heat releasing body in contact with the circuit element. In the ink-jet printer head described in Japanese Patent Application Laid-open No. 2007-83707, a recording head having an actuator is installed on a lower surface side of a bottom plate of ahead holder, exposing nozzles to a lower surface side. The external signal source is installed on an upper surface side of the head holder, and the heat releasing body is arranged inside the head holder.
Therefore, a flexible wiring member, which is drawn from the actuator, has a lower surface of one end portion overlapping with an upper surface of the actuator. The wiring member has the other end portion rising up along an inner wall on a side surface of the head holder, and is drawn to be extended toward the external signal source. Since the circuit element is mounted on an upper surface of the flexible wiring member, the heat releasing body is arranged at an upper surface side of the flexible wiring member, and is in a close contact with the circuit element.
When the flexible wiring member is drawn around as in the ink-jet printer head described in Japanese Patent Application Laid-open No. 2007-83707, an output electrode for connecting to the actuator is formed on the lower surface of the flexible wiring member, and a connecting electrode for mounting the circuit element is formed on the upper surface. Therefore, in the abovementioned one-side wired flexible wiring member, one of the output electrode and the connecting electrode is formed by exposing the electroconductive wire by partially removing the base layer, and the remaining of the output electrode and the connecting electrode is formed by exposing the electroconductive wire by partially removing the covering layer.
However, although polyimide which is used for the base layer has a superior durability, it is not easy to process. Therefore, a high level technology is necessary for forming the electrodes with a fine pitch by removing polyimide, and a manufacturing cost becomes high.